This invention relates to alternating current track circuits for railroads, and while the invention is subject to a wide range of applications, a preferred embodiment of the invention will be particularly described as applied to modulated alternating current track circuits for communicating selected signalling and train control codes through track rails for governing the passage of vehicles.
The present invention is an improvement over currently used alternating current track circuit systems of the general character disclosed in the U.S. Staples Pat. No. 2,884,516, granted Apr. 28, 1959. This patent discloses alternating current track circuits for the several adjoining track sections of a stretch of railway track, each of the track circuits comprising an alternating current code transmitter and an alternating current code receiver connected to opposite ends of the associated track section for detecting occupancy, for communicating signal control rate codes through the track rails and for detecting broken down insulated rail joints which may be used to define boundaries of the several track sections. The alternating current is generally a 100 HZ frequency which is continuously modulated by a code generator to provide time spaced square wave track circuit pulses of 100 HZ alternating current at selected rates of 75, 120 or 180 time spaced pulses per minute. The generating of the square wave pulses tends to generate undesirable harmonics, and the relatively slow 75 rate code is difficult to decode. Phases of the adjoining track circuits are staggered in order to guard against broken down insulated rail joints.
An object of the present invention is to provide alternating current track circuits for the several adjoining track sections of a stretch of railway track having improvements which substantially obviate one or more of the limitations and disadvantages of the described prior systems.
Another object of the present invention is to provide improved means for broken down joint protection.
Another object of the present invention is to reduce to a minimum the generation of harmonic frequencies in generating square wave pulses for communication through the track rails.
Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses.